1. Field of the Invention
The present invention relates generally to soil remediation. An embodiment of the invention relates to a heater element for raising soil temperature during an in situ thermal desorption soil remediation process.
2. Description of Related Art
Contamination of subsurface soils has become a matter of concern in many locations. Subsurface soil may become contaminated with chemical, biological, and/or radioactive contaminants. Contamination of subsurface soil may occur in a variety of ways. Material spills, leaking storage vessels, and landfill seepage of improperly disposed of materials are just a few examples of the many ways in which soil may become contaminated. Contaminants in subsurface soil can become public health hazards if the contaminants migrate into aquifers, into air, or into a food supply. Contaminants in subsurface soil may migrate into the food supply through bio-accumulation in various species that are part of a food chain.
There are many methods to remediate contaminated soil. xe2x80x9cRemediating contaminated soilxe2x80x9d refers to treating the soil to remove soil contaminants or to reduce contaminants within the soil to acceptable levels. A method of remediating a contaminated site is to excavate the soil and to process the soil in a separate treatment facility to eliminate or reduce contaminant levels within the soil. Many problems associated with the method may limit the effectiveness and use of the method. For example, one problem associated with the method is that excavation may generate dust that exposes the surrounding environment and workers to the soil contamination. Also, many tons of soil may need to be excavated to effectively treat even a small contamination site. Equipment cost, labor cost, transport cost, and treatment cost may make the method prohibitively expensive as compared to other available soil remediation methods.
Biological treatment and in situ chemical treatment may also be used to remediate soil. Biological and/or chemical treatment may involve injecting material into the soil. A material injected during a chemical treatment may be a reactant configured to react with the soil contamination to produce non-contaminated reaction products or volatile products that may be easily removed from the soil. The material injected during a chemical treatment may be a flooding agent configured to drive the contamination toward a production well that removes the contaminant from the soil. The flooding agent may be steam, carbon dioxide or other fluid. Soil heterogeneity and other factors may inhibit reduction of contaminant levels in the soil using biological treatment and/or chemical treatment to levels required by governmental regulations.
A process that may be used to remove contaminants from subsurface soil is a soil vapor extraction (SVE) process. An SVE process applies a vacuum to the soil to draw air and vapor through subsurface soil. The vacuum may be applied at a soil/air interface, or the vacuum may be applied through vacuum wells placed within the soil. The air and vapor may entrain and carry volatile contaminants towards the source of the vacuum. Off-gas removed from the soil by the vacuum may include contaminants that were within the soil. The off-gas may be transported to a treatment facility. The off-gas removed from the soil may be processed in the treatment facility to eliminate, or reduce contaminants within the off-gas to acceptable levels. An SVE process may allow contaminants to be removed from soil without the need to move or significantly disturb the soil. An SVE process may operate under roads, foundations, and other fixed structures.
The permeability of the subsurface soil may limit the effectiveness of an SVE process.
Air and vapor may flow through subsurface soil primarily through high permeability regions of the soil. The air and vapor may bypass low permeability regions of the soil. Air and vapor bypassing of low permeability regions may allow large amounts of contaminants to remain in the soil after an SVE process has treated the soil. Reduced air permeability due to water retention, stratified soil layers, and material heterogeneities within the soil may limit the effectiveness of an SVE soil remediation process.
Reduced air permeability due to water retention may inhibit contact of the flowing air with the contaminants in the soil. A partial solution to the problem of water retention is to dewater the soil. The soil may be dewatered by lowering the water table and/or by using a vacuum dewatering technique. These methods may not be effective methods of opening the pores of the soil to admit airflow. Capillary forces may inhibit removal of water from the soil when the water table is lowered. Lowering the water table may result in moist soil. Air conductivity through moist soil is limited.
A vacuum dewatering technique may have practical limitations. The vacuum generated during a vacuum dewatering technique may diminish rapidly with distance from the dewatering wells. The use of a vacuum dewatering technique may not result in a significant improvement to the soil water retention problem. The use of a vacuum dewatering technique may result in the formation of preferential passageways for air conductivity located adjacent to the dewatering wells.
Many types of soil are characterized by horizontal layering with alternating layers of high and low permeability. A common example of a layered type of soil is lacustrine sediments. Thin beds of alternating silty and sandy layers characterize lacustrine sediments. If an SVE well intercepts several such layers, nearly all of the induced airflow occurs within the sandy layers and bypasses the silty layers.
Heterogeneities may be present in subsurface soil. Air and vapor may preferentially flow through certain regions of heterogeneous soil. Air and vapor may be impeded from flowing through other regions of heterogeneous soil. For example, air and vapor tend to flow preferentially through voids in poorly compacted fill material. Air and vapor may be impeded from flowing through overly compacted fill material. Buried debris within fill material may also impede the flow of air through subsurface soil.
In situ thermal desorption (ISTD) may be used to increase the effectiveness of an SVE process. An ISTD soil remediation process involves in situ heating of the soil to raise the temperature of the soil while simultaneously removing off-gas from the soil. Heating the soil may result in removal of contaminants by a number of mechanisms in addition to entrainment of contaminants in an air stream. Such mechanisms may include, but are not limited to: vaporization and vapor transport of the contaminants from the soil; entrainment and removal of contaminants in water vapor; and thermal degradation or conversion of contaminants by pyrolysis, oxidation or other chemical reactions within the soil. In situ heating of the soil may greatly increase the effectiveness of an SVE process.
An ISTD soil remediation process may offer significant advantages over SVE processes and processes that inject drive fluids or chemical and/or biological reactants into the soil. Fluid flow conductivity of an average soil may vary by a factor of 108 throughout the soil due in part to soil heterogeneities and water within the soil. Uniform mass transport through the soil may be a limiting factor in the remediation of a treatment site using an SVE process or a chemical and/or biological treatment of the soil. Thermal conductivity of an average soil may vary by a factor of about two throughout the soil. Injecting heat throughout soil may be significantly more effective than injecting a fluid through the same soil. Heating soil may result in an increase in the permeability of the soil. Heat transferred into the soil may dry the soil. As the soil dries, microscopic and macroscopic permeability of the soil may increase. The increase in permeability of heated soil may allow an ISTD soil remediation process to efficiently remediate the soil throughout a treatment area. The increase in soil permeability may allow in situ remediation of low permeability clays and silts that are not amenable to standard soil vapor extraction processes.
Heat added to contaminated soil may raise the temperature of the soil above vaporization temperatures of contaminants within the soil. If the soil temperature exceeds the vaporization temperature of a soil contaminant, the contaminant may vaporize. Vacuum applied to the soil may be able to draw the vaporized contaminant out of the soil. Even heating the soil to a temperature below vaporization temperatures of the contaminants may have beneficial effects. Increasing the soil temperature may increase vapor pressures of the contaminants in the soil and allow an air stream to remove a greater portion of the contaminants from the soil than is possible at lower soil temperatures.
Most soil includes a large amount of liquid water as compared to contaminants. Raising soil temperature above a vaporization point of water at soil conditions may vaporize water within the soil. The water vapor (steam) may volatize and/or entrain contaminants. Vacuum applied to the soil may remove the volatized and/or entrained contaminants from the soil. Steam vaporization and entrainment of contaminants may result in the removal of medium and high boiling point contaminants from the soil.
In addition to allowing greater removal of contaminants from soil, increasing temperature of the soil may result in the destruction of contaminants in situ. The presence of an oxidizer, such as air, may result in the oxidation of contaminants that pass through high temperature soil. In the absence of oxidizers, contaminants within the soil may be altered by pyrolysis. xe2x80x9cPyrolysisxe2x80x9d refers to chemical change brought about by the action of heat. Vacuum applied to the soil may remove reaction products from the soil.
An ISTD soil remediation system may include four major systems. The systems may be a heating and vapor extraction system, an off-gas collection piping system, an off-gas treatment system, and instrumentation and power control systems.
A heating and vapor extraction system may be formed of wells inserted into the soil for deep soil contamination or of thermal blankets for shallow soil contamination. A combination of wells and thermal blankets may also be used. For example, thermal blankets may be placed at centroids of groups of wells. The thermal blankets may inhibit condensation of contaminants near the soil surface. Soil may be heated by a variety of methods. Methods for heating soil include, but are not limited to, heating substantially by thermal conduction, heating by radio frequency heating, or heating by electrical soil resistivity heating. Thermal conductive heating may be advantageous because temperature obtainable by thermal conductive heating is not dependent on an amount of water or other polar substance within in the soil. Soil temperatures substantially above the boiling point of water may be obtained using thermal conductive heating.
Soil temperatures of about 100xc2x0 C., 200xc2x0 C., 300xc2x0 C., 400xc2x0 C., 500xc2x0 C. or greater may be obtained using thermal conductive heating.
Heaters may be placed in or on the soil to heat the soil. For soil contamination within about 1 meter of the soil surface, a thermal blanket that is placed on top of the soil may apply conductive heat to the soil. A vacuum may be applied to the soil under the blanket through vacuum ports in the blanket. The heaters may operate at about 870xc2x0 C. U.S. Pat. No. 5,221,827 issued to Marsden et al. and incorporated by reference as if fully set forth herein, describes a system that uses thermal blankets.
For deeper contamination, wells may be used to supply heat to the soil and to remove vapor from the soil. The term xe2x80x9cwellsxe2x80x9d refers to heater wells, suction wells, and/or combination heater/suction wells. Heater wells supply thermal energy to the soil. Suction wells may be used to remove off-gas from the soil. Suction wells may be connected to an off-gas collection piping system. A suction well may be coupled to a heater well to form a heater/suction well. In a region adjacent to a heater/suction well, air and vapor flow within the soil may be counter-current to heat flow through the soil. The heat flow may produce a temperature gradient within the soil.
The counter-current heat transfer relative to mass transfer may expose air and vapor that is drawn to a vacuum source to high temperatures as the air and vapor approaches and enters the heater/suction well. A significant portion of contaminants within the air and vapor may be destroyed by pyrolysis and/or oxidation when the air and vapor passes through high temperature zones surrounding and in heater/suction wells. In some ISTD systems, only selected wells may be heater/suction wells. In some ISTD systems, heater wells may be separate from the suction wells. Heaters within heater wells and within heater/suction wells typically operate in a range from about 650xc2x0 C. to about 870xc2x0 C.
Thermal conductive heating of soil may include radiatively heating a well casing, which conductively heats the surrounding soil. Coincident or separate source vacuum may be applied to remove vapors from the soil. Vapor may be removed from the soil through production wells. U.S. Pat. No. 5,318,116 issued to Vinegar et al., which is incorporated by reference as if fully set forth herein, describe ISTD processes for treating contaminated subsurface soil with thermal conductive heating applied to soil from a radiantly heated casing. The heater elements are commercial nichrome/magnesium oxide tubular heaters with Inconel 601 sheaths operated at temperatures up to about 1250xc2x0 C. Alternatively, silicon carbide or lanthanum chromate xe2x80x9cglow-barxe2x80x9d heater elements, carbon electrodes, or tungsten/quartz heaters could be used for still higher temperatures. The heater elements may be tied to a support member by banding straps.
Wells may be arranged in a number of rows and columns. Wells may be staggered so that the wells are in a triangular pattern. Alternately, the wells may be aligned in a rectangular pattern, pentagonal pattern, hexagonal pattern or higher order polygonal pattern. In certain well pattern embodiments, a length between adjacent wells is a fixed distance so that a polygonal well pattern is a regular well pattern, such as an equilateral triangle well pattern or a square well pattern. In other well pattern embodiments, spacing of the wells may result in non-regular polygonal well patterns. A spacing distance between two adjacent wells may range from about 1 meter to about 13 meters or more. A typical spacing distance may be from about 2 meters to about 4 meters.
Wells inserted into soil may be production wells, injection wells and/or test wells. A production well may be used to remove off-gas from the soil. The production well may include a perforated casing that allows off-gas to pass from the soil into the production well. The perforations in the casing may be, but are not limited to, holes and/or slots. The perforations may be screened. The casing may have several perforated zones at different positions along a length of the casing. When the casing is inserted into the soil, the perforated zones may be located adjacent to contaminated layers of soil. The areas adjacent to perforated sections of a casing may be packed with gravel or sand. The casing may be sealed to the soil adjacent to non-producing layers to inhibit migration of contaminants into uncontaminated soil. A production well may include a heating element that allows heat to be transferred to soil adjacent to the well.
In some soil remediation processes, it may be desirable to insert a fluid into the soil. The fluid may be, but is not limited to, a heat source such as steam, a solvent, a chemical reactant such as an oxidant, or a biological treatment carrier. A fluid, which may be a liquid or gas, may be inserted into the soil through an injection well. The injection well may include a perforated casing. The injection well may be similar to a production well except that fluid is inserted into the soil through perforations in the well casing instead of being removed from the soil through perforations in the well casing.
A well may also be a test well. A test well may be used as a gas sampling well to determine location and concentration of contaminants within the soil. A test well may be used as a logging observation well. A test well may be an uncased opening, a cased opening, a perforated casing, or combination cased and uncased opening.
A wellbore for a production well, injection well or test well may be formed by augering a hole into the soil. Cuttings made during the formation of the augered hole may have to be treated separately from the remaining soil. Alternately, a wellbore for a production well, injection well or test well may be formed by driving and/or vibrating a casing or insertion conduit into the soil. U.S. Pat. No. 3,684,037 issued to Bodine and U.S. Pat. No. 6,039,508 issued to White describe devices for sonically drilling wells. Both of these patents are incorporated by reference as if fully set forth herein.
A covering may be placed over a treatment area. The covering may inhibit fluid loss from the soil to the atmosphere, heat loss to the atmosphere, and fluid entry into the soil. Heat and vacuum may be applied to the cover. The heat may inhibit condensation of contaminants on the covering and in soil adjacent to the covering. The vacuum may remove vaporized contaminants from the soil adjacent to a soil/air interface to an off-gas treatment system.
An off-gas collection piping system may be connected to suction wells of a heating and vapor extraction system. The off-gas collection piping system may also be connected to an off-gas treatment system so that off-gas removed from the soil may be transported to the treatment system. Typical off-gas collection piping systems are made of metal pipe. The off-gas collection piping may be un-heated piping that conducts off-gas and condensate to the treatment facility. Alternately, the off-gas collection piping may be heated piping that inhibits condensation of off-gas within the collection piping. The use of metal pipe may make a cost of a collection system expensive. Installation of a metal pipe collection system may be labor and time intensive.
Off-gas within a collection piping system may be transported to an off-gas treatment system. The treatment system may include a vacuum system that draws off-gas from the soil. The treatment system may also remove contamination within the off-gas to acceptable levels. The treatment facility may include a reactor system, such as a thermal oxidizer, to eliminate contaminants or to reduce contaminants within the off-gas to acceptable levels. Alternately, the treatment system may use a mass transfer system, such as passing the off-gas through activated carbon beds, to eliminate contaminants or to reduce contaminants within the off-gas to acceptable levels. A combination of a reactor system and a mass transfer system may also be used to eliminate contaminants or to reduce contaminants within the off-gas to acceptable levels.
Instrumentation and power control systems may be used to monitor and control the heating rate of the heater system. The instrumentation and power control system may also be used to monitor the vacuum applied to the soil and to control of the operation of the off-gas treatment system. Electrical heaters may require controllers that inhibit the heaters from overheating. The type of controller may be dependent on the type of electricity used to power the heaters. For example, a silicon controlled rectifier may be used to control power applied to a heater that uses a direct current power source, and a zero crossover electrical heater firing controller may be used to control power applied to a heater that uses an alternating current power source.
A barrier may be placed around a region of soil that is to be treated. The barrier may include metal plates that are driven into the soil around a perimeter of a contaminated soil region.
A top cover for the soil remediation system may be sealed to the barrier. The barrier may limit the amount of air and water drawn into the treatment area from the surroundings. The barrier may also inhibit potential spreading of contamination from the contaminated region to adjacent areas.
An ISTD soil remediation process may be used to treat a region of contaminated soil. The process may be implemented using system components that are readily available, relatively inexpensive, and easy to install. The process may be implemented using heaters, a collection piping system, a control system, and a treatment facility. System components of the process may be made of readily available materials. The process may be easy to install, control and operate as compared to conventional ISTD soil remediation processes.
Heaters for an ISTD soil remediation process may include electrical resistance heater elements. In certain embodiments of soil remediation systems, heater elements used to heat soil may be structurally self-supporting, bare metal, radiant heating elements that are suspended within a casing or within an opening in the soil. In certain embodiments of soil remediation systems, heater elements may be structurally self-supporting members, conductive heating elements that are placed within a formation or within a casing. Bare metal heaters may advantageously be readily available. Also, using bare metal heaters may advantageously eliminate cost and installation time associated with buying and installing supporting members for heater wells.
Heater sections of the heater elements may be formed of high temperature, chemical resistant metal if the heater sections are to be exposed to off-gas during soil remediation. Alternately, the heater elements may be formed of less expensive, less chemically resistant metal if the heater element is enclosed in a heater element casing. The heater section dissipates heat when the heater element is connected to a power source. The metal that forms the heater section may be, but is not limited to, stainless steel, Incoloy(copyright), or Nichrome(copyright). The specific metal used to form the heater section of a strip heater may be chosen based on cost, temperature of the soil remediation process, electrical properties of the metal, physical properties of the metal, chemical resistance properties of the metal, and other factors. Heater elements of an ISTD soil remediation system may be formed, or partially formed, from materials having resistivity properties allowing for self regulation of heat generated by the heater element. The use of a self regulating heater element may advantageously obviate the need for controllers for the heaters of the ISTD soil remediation system.
Heater elements may be configured to conductively heat surrounding material. The surrounding material may be soil and/or packing material. A heater section of a conductive heater element may be bare metal. The heater element may be allowed to thermally expand upwards when heated. The conductive heater element may be directly driven into the soil. Fill material may be used to pack the heater element within the casing. In an embodiment, the heater element is a metal strip that is sonically or mechanically driven into the soil to form a xe2x80x9cUxe2x80x9d shape. A vacuum well casing may be placed between legs of the heater element. In alternate embodiments, heater elements and/or vacuum well casings may be placed within drilled openings in the soil. In other embodiments, heater elements may be placed within trenches formed in the soil. A space between legs of the heater element and/or the vacuum well casing may be packed with sand, gravel, or other packing material.
A conductive heater element may need to be made of a material having high corrosion resistance at high temperatures because the heater element may come into direct contact with off-gas and other fluid within the soil. Alternately, a conductive heater element may be packed into a heater casing with sand, gravel, or other packing material. The packing material may conductively transfer heat to the heater element well casing. The heater element casing may transfer heat to additional packing material and/or soil. The packing material may also inhibit the heater element from contacting the heater casing wall. Alternately, electrically insulating spacers may be periodically placed along a length of the heater element to inhibit contact between the heater element and the casing wall, and between legs of the heater element. Compared to conventional radiant heating, a heater strip may operate at a lower temperature for the same power input. The lower operating temperature of the heater element may lengthen a lifetime of a heater element and may increase reliability of the heating system.
A heater section of a conductive heater element may have a large cross section area as compared to a cross sectional area of a conventional radiative heater element. The large cross sectional area of the heater section may result in a smaller electrical resistance for the heater element as compared to conventional radiative heaters of equivalent length. The smaller electrical resistance may allow several strip heaters to be connected in series. The ability to connect several strip heaters in series may greatly simplify wiring requirements for an ISTD soil remediation system. The large cross sectional area of the heater section may also allow a large contact area between the heater section and material placed adjacent to the heater section. The large contact area may promote dissipation of heat produced in the strip heater into surrounding soil.
Fill material for a conductive heating element that is placed directly in the soil may include a catalyst material, such as alumina, that enhances the thermal breakdown of contaminants. A heater/suction well may be formed by inserting a perforated casing between legs of a conductive heating element. Attaching the perforated casing to a vacuum source allows vacuum to remove vapor from the soil as off-gas. Positioning the casing between legs of a U-shaped heater element allows the off-gas to pass through a high temperature zone before being removed from the soil. Passing the off-gas through the high temperature zone may result in thermal degradation of contaminants by oxidation and/or pyrolysis of contaminants within the off-gas.
Heater elements may be configured to radiatively heat a heater casing. A radiative heater element may be bare metal. The heater element may be suspended within a casing or suspended within an opening in the soil to be remediated. The cross sectional area, length and type of metal used to form the radiative heater element may allow for suspension of the heater element without securing the heater element to a support member periodically along a length of the heater element. Suspending a heater element may allow the element to thermally expand downwards when heated. Insulating spacers may be periodically spaced along a length of the heater element to inhibit the heater element from contacting a wall of the casing. The insulating spacers may also inhibit contact between legs of the heater element. A fluid, such as helium, may be placed in the casing to promote conductive heat transfer from the heater element to the casing. The heater casing wall may be textured, blackened, or otherwise treated to increase emissivity of the heater casing. An increased emissivity may improve radiative heat transfer between the heater element and the heater casing.
A conductive or radiative heater element may be formed with a variable cross sectional area, and/or with sections made of material having different resistance properties, so that greater heat dissipation occurs at certain portions of the heater element (sections having a smaller cross sectional area and/or higher electrical resistance) than at other portions of the heater element. A local high heat dissipation section of the heater element may be positioned adjacent to soil that requires extra heat dissipation, such as wet soil or sections of soil adjacent to the top and bottom of the heater element. Areas adjacent to the top and bottom of a heater element may need extra heating to counteract end loss heat effects. Selected portions of a heater element may be formed with sections that have a large cross sectional area. Large cross sectional area sections of a heater element may be placed adjacent to an overburden and/or uncontaminated soil layers.
A heater element casing may be driven into the soil, packed into soil, or packed within a second casing that is placed within the soil. The second casing may be a vacuum well casing. Packing material between the second casing and the heater element casing may be sufficiently porous to allow off-gas to easily flow into and out of an annular space between the heater casing and the vacuum casing. Placing a heater element in a heater element casing may allow the heater element to be made of a relative inexpensive, non-corrosion resistant material because off-gas will not come into direct contact with the heater element. The heater element casing may be made of a material that has sufficient corrosion resistance to resist breakthrough corrosion during the estimated time needed to complete soil remediation.
For low depth soil contamination, heater elements, or heater elements positioned within casings, may be placed within trenches within the contaminated soil. Vacuum drawn on the soil surface and/or vacuum drawn within the soil may be used to remove off-gas from the soil. Forming trenches and placing heater elements within trenches may be less expensive than placing heater elements in the soil by driving, vibrating, or placing the heater elements within drilled openings in the soil. For deeper soil contamination, the heater elements may be vibrated or driven into the soil, or the heater elements may be placed within drilled openings. The heater elements may be substantially vertically positioned with respect to the ground surface, or the heater elements may be positioned in a slanted or arcing orientation within the soil. Coincident or separately positioned vacuum wells may be used to remove off-gas from the soil.
Cased or uncased heater elements may be of any desired cross sectional shape, including, but not limited to, triangular, rectangular, square, hexagonal, ellipsoidal, round, or, ovate. In certain heater element embodiments, radiant heater elements are made of rod stock. In certain heater element embodiments, conductive heater elements are formed of rod stock or bar stock.
Simple geometry and use of common stock material may advantageously result in least a 50% cost reduction in heater element material cost and formation as compared to conventional heater elements. Conductive heater elements placed directly in the soil may advantageously eliminate cost associated with a heater element casing. Heater elements made of material that has self regulating heating characteristics may advantageously eliminate the need for heater element controllers.
Installation costs for conductive heater elements that are directly positioned within the soil may be reduced by 75% or more as compared to installation costs for conventional heater elements. Installation costs for heater/suction wells that include conductive heater elements that are directly placed or packed within the soil may be reduced by 50% or more as compared to installation costs for conventional heater/suction wells. Also, installation time for heater wells or heater/suction wells may be significantly reduced for conductive heater elements that are positioned in the soil as compared to installation time for conventional heater elements or heater/suction wells. For example, placing a cased heater in an augered hole and connecting the heater element to a power source may take about six hours. Directly installing a conductive heater element and connecting the heater to a power source may take about one sixth of an hour.
A collection system may connect suction wells of a soil remediation system to a treatment facility. The collection system may include hoses and a polymer vacuum manifold instead of conventional metal piping. The hoses may be high temperature hoses. The hoses may be, but are not limited to high temperature rubber hoses, high temperature silicone rubber hoses, or coated rubber flexible metal hoses. Collections systems typically operate under vacuum; therefore, the hoses need to have structural strength that inhibits collapse of the hoses. The hoses may be double walled hose or a steel reinforced hose. The vacuum manifold may be plastic piping, such as chlorinated polyvinyl chloride (CPVC) piping. Off-gas passing through a hose has a residence time within the hose due to the length of the hose. The residence time may be sufficiently long to allow the off-gas to cool to a temperature within the working temperature limits of the vacuum manifold piping. A hose may be from about 1 m to over 10 m in length. Longer or shorter lengths may be used to meet specific operational requirements.
Use of a hose and plastic piping collection system may result in lower costs, simplified on-site construction, and lower transportation costs as compared to conventional metal piping collection systems. The hose and plastic piping collection system may not be insulated and heated to prevent condensation of the off-gas. The collection system may use an initial riser and gravity to flow condensed off-gas to a trap or to a treatment facility. An unheated collection system greatly reduces cost, installation time, and operating cost of the collection system. The hose may be rolled into coils for transportation. Plastic piping may be purchased locally near the site. Hose and plastic piping are easily cut to size on-site and are connectable by solvent gluing. The need to have precise positioning of metal pipes is eliminated. Also, hose and plastic piping are lightweight and do not require machinery to lift and position during installation. For soil contaminated with chlorinated compounds, off-gas removed from the soil may contain significant amounts of hydrogen chloride. Off-gas may contain other corrosive chemicals as well. The use of hose and plastic piping may advantageously obviate the need to have expensive, chemically resistant metal piping to handle corrosive off-gas.
A treatment facility processes off-gas from the soil to remove, reduce, concentrate, or otherwise treat contaminants within the off-gas. A treatment facility may also provide vacuum that removes the off-gas from the soil. The treatment facility may include a condenser that separates the off-gas into a liquid stream and a vapor stream. The liquid stream and the vapor stream may be separately processed to remove, reduce or concentrate contaminants. The liquid stream may be treated using a separator and/or an activated carbon bed. The separator may produce an aqueous phase and an organic (hydrocarbon) phase. The vapor stream may be treated using an activated carbon bed and/or an air stripper. Depending on the nature of the soil contamination, a majority of contaminants may be destroyed by pyrolysis and/or oxidation within the soil or within heater/suction wells. The remaining contamination may be concentrated, stored and transported offsite; may be absorbed or adsorbed in mass transfer systems; or may be destroyed on site in a reactor system. Depending on the type of contamination, the reactor system may be a chemical treatment system and/or a thermal treatment system. In some soil remediation system embodiments, a contaminant treatment portion of the treatment facility may only need to operate during an initial start up period when temperatures of heater elements are rising to operation temperatures. After the heating elements reach operating temperatures, the contaminants may be destroyed within the soil or within wells by oxidation and/or pyrolysis.
Previous treatment facilities may have required the use of a thermal oxidizer. Removing the thermal oxidizer from the treatment facility eliminates the large capital cost, transportation costs, and operating expenses associated with the thermal oxidizer. The elimination of the thermal oxidizer may allow the soil remediation process to be run unattended. A site supervisor may periodically check the system and perform normal maintenance functions at the site to ensure proper operation of the soil remediation system. Continuous manned operation of the in situ soil remediation process may not be required.